INDIRECT INJURIES CAUSED BY INSECTS. 119 



mouth. 1 The insects injurious to deciduous trees mostly leave the fir and 

 pine tribes untouched ; but these on the other hand, are subject to have 

 their foliage ravaged by a great variety of insect enemies peculiar to them- 

 selves, to some extent in this country, but far more on the Continent, as 

 by the larvae of various moths (Dendrolimus pini, Psilura monacha, Achatia 

 piniperda, Bupalus piniarius, Orthotcenia turionana and resinella, &c.) ; and 

 of not fewer than three species of saw-fly (ILophyrus pini and rufus and 

 Pamphilius erythrocephala) . 2 The injury thus caused to trees by insects 

 is not confined to the mere loss of their leaves for one season ; for it oc- 

 casions them to draw upon the funds of another, by sending forth prema- 

 ture shoots, and making gems unfold, that, in the ordinary course, would 

 not have put forth their foliage till the following year. 



Other insects, though they do not entirely devour the leaves of trees 

 and plants, yet considerably diminish their beauty. Thus, for instance, 

 sometimes the subcutaneous larvae undermine them, when the leaf ex- 

 hibits the whole course of their labyrinth in a pallid, tortuous, gradually 

 dilating line at others, the Tortrices disfigure them by rolling them up, 

 or the leaf-cutter bees by taking a piece out of them, or certain Tinecs 

 again by eating their under surface, and so causing them to wither either 

 partially or totally. You have doubtless observed what is called the honey- 

 dew upon the maple and other trees, concerning which the learned Roman 

 naturalist Pliny, gravely hesitates whether he shall call it the sweat of the 

 heavens, the saliva of the stars, or a liquid produced by the purgation of the 

 air ! ! 3 Perhaps you may not be aware that it is a secretion of Aphides, 

 whose excrement has the privilege of emulating sugar and honey in sweet- 

 ness and purity. It, however, often tarnishes the lustre of those trees in 

 which these insects are numerous, and is the lure that attracts the swarms 

 of ants which you may often see travelling up and down the trunk of the 

 oak and other trees. 4 The larch in particular is inhabited by an Aphis 

 transpiring a waxy substance like filaments of cotton : this is sometimes so 

 infinitely multiplied upon it as to whiten the whole tree, which often 

 perishes in ^consequence of its attack. The beech is infested by a similar 

 one. Some animals also of this genus inhabiting the poplar, elm, lime, 

 and willow, reside in galls they have produced, that disfigure the leaves or 

 their footstalks. Perhaps those resembling fruit, or flowers, or moss, pro- 

 duced by the Aphis of the fir (Aphis abietis), the different species of gall . 

 gnats (Ceddomyia\ or occasioned by the puncture and oviposition of the 

 various kinds of gall-flies (Cynips], may be regarded rather as an ornament 



1 Stedman, ii. 142. 



2 Kollar, on Ins. inj. to Gardeners, &c. 323 356. 



3 Hist. Nat. 1. xi. c. 12. 



4 It is contended by some observers, that besides the honey-dew caused by Aphides, 

 there is another arising solely from a morbid exudation of the saccharine juices of 

 trees. This is certainly possible ; but I may observe, that in the course of more than, 

 thirty years which I have attended to this subject (seven of them spent on the Con- 

 tinent, where the greater heat might be supposed likely to cause morbid vegetable 

 action), I have never met with any honey-dew which did not seem to me very 

 clearly referable to Aphides as its origin ; though, from the circumstance of their 

 having been all swept away by the attacks of their natural enemies and other causes, 

 while their saccharine excretion remains on the leaves for weeks' in a dry time, and 

 after being moistened by a slight dew may have every appearance of being a recent 

 morbid exudation, and may, even after very copious dews, fall on the ground, a 

 casual observer may often be plausibly led to a different conclusion. 



1 4 



